TRINBMA ENCHELYS. 89 



WAILES in Scott. Natur. 1912, p. 61 b ; in Trans. Liverp. Biol. Soc. 



XXVI (1912), p. 20 ; in Jrn. Linn. Soc. XXXII (1912), pp. 126, 152 ; 



loc. cit. (1913), p. 213; in Murray's Nat. Hist. Bolivia and Peru (1913), 



pp. 32, 40 ; in Naturalist, 1913, p. 148. 



CUNHA in Mem. Inst. Oswaldo Cruz, V (1913), pp. 101, 102. 

 SCHMIDT in Arch. Protist. XXIX (1913), p. 222. 

 Trinema 

 DELAGE & HEROUABD Traite Zool. concrete, I (1896), p. 112, f. 142. 



Test hyaline, oviform, compressed anteriorly, formed 

 of circular silicious plates ; aperture circular, subter- 

 minal, oblique and invaginated; plasma granular, 

 partly filling the test ; nucleus placed posteriorly, con- 

 taining a central nucleole ; one or two contractile 

 vesicles usually present ; pseudopodia attenuate, radi- 

 ating, often long, sometimes numerous. 



Length 32-103 //,; breadth 15-60 /x; aperture 6-20 p 

 in diameter ; scales 4-12 /x, in diameter ; nucleus 6-12 /x 

 in diameter. 



Habitat. Mosses, sphagnum, and aquatic vegetation. 

 Generally distributed. 



Mosses may be looked upon as the usual habitat of 

 this species, and from 40-60 /A as the ordinary limits 

 of length when so occurring ; in sphagnum and 

 among aquatic vegetation it occurs less numerously 

 but of larger average size, and individuals up to 80 JJL 

 in length are not uncommon ; above this size they are 

 rare and confined to limited areas. 



The circular plates forming the test may be nearly 

 flat or have a considerable convexity, that is be shaped 

 like a watch-glass; they may be imbricated or con- 

 nected together by rings of small circular or oval 

 markings; the plates bordering the anterior of the 

 aperture are usually small and circular ; the invagina- 

 tion around it is formed by a number of small, circular, 

 curved rods 0'5 to 0'75/A in diameter cemented into a 

 ring; the aperture is often only approximately circular 

 and may show traces of seven to nine sides, according to 

 the number of plates bordering it ; the invagination is 

 sometimes reversed, as in the genus Arcella, but tests 

 with evaginated apertures are rare. The angle which 



